Bumper assembly including an energy absorber

ABSTRACT

A bumper assembly ( 20 ) for an automotive vehicle is described. The bumper assembly comprises a beam ( 24 ) and an energy absorber ( 22 ). In one example embodiment, the energy absorber is tunable for meeting predetermined criteria for both low speed and pedestrian impacts.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to bumpers and, moreparticularly, to energy absorbing vehicle bumper systems.

[0002] A known standard which bumper systems often are designed to meetis the United States Federal Motor Vehicle Safety Standard (FMVSS). Forexample, some energy absorbing bumper systems attempt to reduce vehicledamage as a result of a low speed impact by managing impact energy andintrusion while not exceeding a rail load limit of the vehicle. Inaddition, some bumper systems attempt to reduce pedestrian injury as aresult of an impact.

[0003] A bumper system typically includes a beam that extends widthwiseacross the front or rear of a vehicle and is mounted to rails thatextend in a lengthwise direction. The beam typically is steel, and thesteel beam is very stiff and provides structural strength and rigidity.To improve the energy absorbing efficiency of a bumper system, somebumper systems also include shock absorbers.

[0004] The efficiency of an energy absorbing bumper system, or assembly,is defined as the amount of energy absorbed over distance, or the amountof energy absorbed over load. A high efficiency bumper system absorbsmore energy over a shorter distance than a low energy absorber. Highefficiency is achieved by building load quickly to just under the railload limit and maintaining that load constant until the impact energyhas been dissipated.

[0005] To improve the energy absorbing efficiency, shock absorberssometimes are positioned, for example, between the steel bumper beam andthe vehicle rails. The shock absorbers are intended to absorb at leastsome of the energy resulting from an impact. Adding shock absorbers to abumper assembly results in an added cost and complexity as compared to asteel beam. The shocks also add weight to the bumper assembly, which isalso undesirable since such added weight may reduce the overall fuelefficiency of the vehicle.

[0006] Other known energy absorbing bumper systems include a foam energyabsorber. Foam based energy absorbers typically have slow loading uponimpact, which results in a high displacement. Further, foams areeffective to a sixty or seventy percent compression, and beyond thatpoint, foams become incompressible so that the impact energy is notfully absorbed. The remaining impact energy is absorbed throughdeformation of the beam and/or vehicle structure.

BRIEF SUMMARY OF THE INVENTION

[0007] In one aspect, a bumper system comprising a beam configured toattach to vehicle rails and an energy absorber coupled to the beam isprovided. The energy absorber is tunable for meeting predeterminedcriteria for both low speed and pedestrian impacts.

[0008] In another aspect, a bumper assembly for an automotive vehicle isprovided. The bumper assembly comprises a beam configured to attach tovehicle rails, an energy absorber, and a fascia attachable to the energyabsorber to substantially envelop the beam and energy absorber. Theenergy absorber is tunable for meeting predetermined criteria for bothlow speed and pedestrian impacts.

[0009] In yet another aspect, an energy absorber for a vehicle bumpersystem is provided. The energy absorber is tunable for meetingpredetermined criteria for both low speed and pedestrian impacts andcomprises a flanged frame and a body extending from the frame. The bodycomprises a plurality of lobes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is an exploded perspective view of one embodiment of abumper assembly including an energy absorber.

[0011]FIG. 2 is a front perspective view of the energy absorber.

[0012]FIG. 3 is a rear perspective view of the energy absorber shown inFIG. 2.

[0013]FIG. 4 an enlarged view of a portion of the energy absorber shownin FIGS. 2 and 3.

[0014]FIG. 5 is a top view of the lobe shown in FIG. 4.

[0015]FIG. 6 is a cross sectional view through a center of an energyabsorber lobe shown in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0016] A bumper system that includes a tunable energy absorber isdescribed below in detail. In an example embodiment, an energy absorberof the non-foam type is attached to a beam. The beam is fabricated, forexample, from steel, aluminum, or glass mat thermoplastic (GMT). Theenergy absorber, in the example embodiment, is fabricated from Xenoy®material and is tunable so as to meet desired impact criteria, e.g.,pedestrian and low speed impacts. More particularly, a front portion ofthe energy absorber is tuned, and tunable, to absorb pedestrian leg formimpact, and a rear portion of the energy absorber is tuned, and tunable,for low speed barrier and pendulum impact. Impact forces during thespecified types of impacts are maintained just below a predeterminedlevel by deforming the energy absorber and beam until the kinetic energyof the impact event has been absorbed. When the impact is over, theenergy absorber returns substantially to its original shape and retainssufficient integrity to withstand subsequent impacts.

[0017] Although the bumper system is described below with reference tospecific materials (e.g. Xenoy® material (commercially available fromGeneral Electric Company, Pittsfield, Mass.) for the energy absorber),the system is not limited to practice with such materials and othermaterials can be used. For example, the beam need not necessarily be asteel, aluminum, or GMT compression molded beam, and other materials andfabrication techniques can be utilized. Generally, the energy absorberis selecting from materials that result in efficient energy absorption,and the beam materials and fabrication technique are selected to resultin a stiff beam.

[0018]FIG. 1 is an exploded perspective view of one embodiment of abumper system 20. System 20 includes an energy absorber 22 and a beam24. Energy absorber 22 is positioned between beam 24 and a fascia 26which, when assembled, form a vehicle bumper. As should be understood bythose skilled in the art, beam 24 is attached to lengthwise extendingframe rails (not shown).

[0019] Fascia 26 typically is generally formed from a thermoplasticmaterial amenable to finishing utilizing conventional vehicle paintingand/or coating techniques. Generally, fascia 26 envelops both energyabsorber 22 and reinforcing beam 24 such that neither component isvisible once attached to the vehicle.

[0020] Beam 24, in the example embodiment, is fabricated from extrudedaluminum. In other embodiments, beam 24 is fabricated from roll formedsteel or a compression molded glass mat thermoplastic (GMT). Beam 24 canhave one of multiple geometries, including being configured as aB-section, a D-section, an I-beam, or having a C or W cross-sectionalshape. The geometry of beam 24 is selected to provide a desired sectionmodulus depending on the particular application in which the beam is tobe used. Beam 24 includes rail attachment openings 28 so that bolts (notshown) can pass therethrough to secure bumper system 20 to the framerails.

[0021] Energy absorber 22 includes a frame 50 having first and secondlongitudinally extending flanges 52 and 54, respectively, which overlapbeam 24. Flange 52 is u-shaped and flange 54 includes a finger 56 whichforms a snap fit with beam 24, i.e., finger 56 snaps over an end of beam24. Absorber 22 further includes a body 58 that extends outward fromframe 50. The specific configuration of body 58 is illustrated anddescribed below in connection with FIGS. 2, 3, and 4.

[0022] Referring now to FIGS. 2, 3, and 4, energy absorber body 58,sometimes referred to herein as a front portion, includes a firsttransverse wall 62 and a second transverse wall 64 having a plurality oftunable crush boxes 66 extending therebetween. Transverse walls 62, 64are rippled and include alternating raised areas 68 and depressed areas70 which provide the transverse walls with an added degree of stiffnessto resist deflection upon impact. Transverse walls 62 and 64 furtherinclude a plurality of windows or openings 71. The width and depthdimensions of the ripples, as well as the dimensions of openings 71, canbe modified to achieve different stiffness characteristics as desired.Crush boxes 66 include side walls 72, an outer wall 74, and open areas76 that extend to inner frame 50.

[0023]FIG. 4 is a perspective view of a portion of energy absorber 22.Absorber 22 includes a plurality of lobes 80 (three and one half lobesare shown in FIG. 4). In the example embodiment, energy absorber 22 hasseven lobes 80. Of course, in other embodiments, fewer or more lobes canbe incorporated into the energy absorber.

[0024] In the example embodiment, side walls 72 and traverse walls 62and 64 vary linearly in thickness from a first front-most portion 82 toa rearmost portion 86. In one embodiment, the wall thickness varies fromabout 1 millimeter (mm) to about 7 mm, in another embodiment, from about1.5 mm to about 5 mm, and still another embodiment, from about 2.5 mm toabout 3.5 mm. In further embodiments, the thickness of the walls isconstant from front-most portion 82 to rearmost portion 86 and isbetween about 1 mm to about 7 mm. In still further embodiments, thethickness of the walls are stepped. Particularly, the thickness of thewalls of front-most portion 82 is constant and the thickness of thewalls of rearmost portion 86 is constant with the walls of rearmostportion 86 thicker than the walls of front-most portion 82.

[0025] Energy absorber 22 is tunable in that by selecting a thickness ofeach portion 82 and 86, the response of energy absorber 22 can bealtered depending on the application in which absorber 22 is used. Forexample, front portion 82 of energy absorber 22 is tuned, and tunable,to absorb pedestrian leg form impact, and rear portion 86 is tuned, andtunable, for low speed and pendulum impact.

[0026] Referring to FIGS. 5 and 6, which are top and cross sectionalviews of lobe 80, a number of dimensions are illustrated by the lettersA, B, C, D, E, and F. Each such dimension is selectable so that absorber22 is tunable to a particular application. Example ranges of thedimensions illustrated in FIGS. 5 and 6 are set forth below.

[0027] A ranges from about 91 degrees to about 98 degrees.

[0028] B ranges from about 91 degrees to about 98 degrees.

[0029] C ranges from about 30 degrees to about 90 degrees.

[0030] D ranges from about 20 mm to about 90 mm.

[0031] E ranges from about 10 mm to about 40 mm.

[0032] F ranges from about 50 mm to about 120 mm.

[0033] Each lobe 80 can, of course, have any one of a number ofdifferent geometries depending on the impact energy requirements for thevehicle. Each lobe 80 has an axial crush mode in both barrier andpendulum impacts according to Federal Motor Vehicle Safety Standard(FMVSS) and also has a stiffness tunability in order to meet the desiredimpact load deflection criteria. That is, the wall thicknesses asillustrated in FIG. 4 and the dimensions illustrated in FIGS. 5 and 6can be selected for any given application in an effort to meet thetargeted criteria.

[0034] For example, the walls may have a thickness that broadly rangesfrom about 1.0 mm to about 7.0 mm. More specifically, for certain lowspeed or pedestrian impact applications the nominal wall thickness maygenerally range from about 1.0 mm to about 5.0 mm and for otherapplications, particularly those for a 5 mph FMVSS system, the nominalwall thickness for the side and rear walls would more likely be in therange of about 2.5 mm to 7.0 mm.

[0035] Another aspect in appropriately tuning energy absorber 22 is theselection of the thermoplastic resin to be employed. The resin employedmay be a low modulus, medium modulus or high modulus material as needed.By carefully considering each of these variables, energy absorbersmeeting the desired energy impact objectives can be manufactured.

[0036] The characteristics of the material utilized to form energyabsorber 22 include high toughness/ductility, thermally stable, highenergy absorption capacity, a good modulus-to-elongation ratio andrecyclability. While the energy absorber may be molded in segments, theabsorber also can be of unitary construction made from a tough plasticmaterial. An example material for the absorber is Xenoy material, asreferenced above. Of course, other engineered thermoplastic resins canbe used. Typical engineering thermoplastic resins include, but are notlimited to, acrylonitrile-butadiene-styrene (ABS), polycarbonate,polycarbonate/ABS blend, a copolycarbonate-polyester,acrylic-styrene-acrylonitrile (ASA),acrylonitrile(ethylene-polypropylene diamine modified)-styrene (AES),phenylene ether resins, blends of polyphenylene ether/polyamide (NORYLGTX® from General Electric Company), blends of polycarbonate/PET/PBT,polybutylene terephthalate and impact modifier (XENOY® resin fromGeneral Electric Company), polyamides, phenylene sulfide resins,polyvinyl chloride PVC, high impact polystyrene (HIPS), low/high densitypolyethylene (l/hdpe), polypropylene (pp) and thermoplastic olefins(tpo).

[0037] While the invention has been described in terms of variousspecific embodiments, those skilled in the art will recognize that theinvention can be practiced with modification within the spirit and scopeof the claims.

What is claimed is:
 1. A bumper system (20), comprising: a beam (24)configured to attached to vehicle rails; and an energy absorber (22)coupled to said beam, said energy absorber being tunable for meetingpredetermined criteria for both low speed and pedestrian impacts.
 2. Abumper system (20) according to claim 1 wherein said energy absorber(22) is injection molded.
 3. A bumper system (20) according to claim 1wherein said beam (24) is at least one of steel, aluminum,thermoplastic, and glass mat thermoplastic.
 4. A bumper system (20)according to claim 1 wherein said energy absorber (22) comprises aflanged frame (50) for attachment to said beam (24) and a body (58)extending from said frame, said body comprising a plurality of lobes(80).
 5. A bumper system (20) according to claim 4 wherein at least oneof said lobes (80) comprises first and second spaced transverse walls(62, 64).
 6. A bumper system (20) according to claim 5 wherein saidfirst and second spaced transverse walls (62, 64) are rippled, andwherein each said lobe (80) comprises at least one crush box (66).
 7. Abumper system (20) according to claim 6 wherein said crush box (66)comprises side and outer walls (72,74).
 8. A bumper system (20)according to claim 7 wherein said side and outer walls (72,74) comprisewindows (71) of predetermined shape and size.
 9. A bumper assembly (20)for an automotive vehicle comprising: a beam (24) configured to attachto vehicle rails; an energy absorber (22) coupled to said beam, saidenergy absorber being tunable for meeting predetermined criteria forboth low speed and pedestrian impacts; and a fascia attachable (26) tosaid energy absorber to substantially envelop said beam and said energyabsorber.
 10. A bumper assembly (20) according to claim 9 wherein saidenergy absorber (22) is injection molded.
 11. A bumper assembly (20)according to claim 9 wherein said beam (24) comprises at least one ofsteel, aluminum, thermoplastic, and glass mat thermoplastic.
 12. Abumper assembly (20) according to claim 9 wherein said energy absorber(22) comprises a flanged frame (50) for attachment to said beam (24) anda body (58) extending from said frame, said body comprising a pluralityof lobes (80), each said lobe comprising first and second spacedtransverse walls (62, 64).
 13. A bumper assembly (20) according to claim12 wherein said first and second spaced transverse walls (62. 64) arerippled, and wherein each said lobe (80) comprises at least one crushbox (66), each said crush box comprising side and outer walls (72, 74).14. A bumper assembly (20) according to claim 13 wherein said side andouter walls (72, 74) comprise windows (71) of predetermined shape andsize.
 15. An energy absorber (22) for a vehicle bumper system (20), saidenergy absorber being tunable for meeting predetermined criteria forboth low speed and pedestrian impacts and comprising a flanged frame(50) and a body (58) extending from said frame, said body comprising aplurality of lobes (80).
 16. An energy absorber (22) according to claim15 wherein said energy absorber is injection molded.
 17. An energyabsorber (22) according to claim 15 wherein at least one of said lobes(80) comprises first and second spaced transverse walls (62, 64).
 18. Anenergy absorber (22) according to claim 17 wherein said first and secondspaced transverse walls (62, 64) are rippled, and wherein each said lobe(80) comprises at least one crush box (66), each said crush boxcomprising side and outer walls (72, 74).
 19. An energy absorber (22)according to claim 18 wherein said side and outer walls (72, 74)comprise windows (71) of predetermined shape and size.